1. Field of the Invention
The present invention relates to a projection television receiving apparatus, and more particularly such apparatus capable of generating an image corresponding to a video signal by means of a light modulator such as a liquid crystal light valve, and projecting the image into a projection plane such as a screen.
2. Related Background Art
Image projectors utilizing a liquid crystal light valve are already disclosed for example in the Japanese Patent Application Laid-Open No. 61-13885, No. 62-125791 and No. 63-106785, but manual focusing of the image on the screen is required in these projectors because they lack the automatic focusing function which is already employed, for example, in the still cameras, video cameras, slide projectors or the like.
On the other hand, the present applicant already proposed, in the Japanese Patent Appln. Laid-Open No. 63-253342, a projector capable of measuring the distance between the projector itself and the screen by a range finding device utilizing infrared light or ultrasonic wave, identifying the image size on the screen from the result of distance measurement, and regulating the luminance of the projected image according to the image size. However this projector still requires manual focusing the image on the screen, since it lacks the automatic focusing function.
Recently there are commercialized projection television receiving apparatus utilizing portable projectors, but the user can enjoy a clear image only after exactly positioning the projector and the screen and focusing the image onto the screen.